1. Field of the Invention
The present invention relates to an endoscope apparatus that controls various imaging modes and to a control method thereof.
2. Description of the Related Art
In recent years, in the field of electronic endoscope apparatuses using solid-state imaging devices, spectral imaging, in other words, electronic endoscope apparatuses with built-in narrow-band filters (Narrow Band Imaging—NBI) received attention. The Narrow Band Imaging uses narrow-band-pass filters in combination based on spectral reflectance in digestive organs (gastric mucosa (mucosa of stomach), or the like). In the NBI electronic endoscope apparatuses, three band-pass filters that pass light of narrow (wavelength) bands are provided instead of plane-sequential rotary filters of R (red), G (green), and B (blue). In the NBI electronic endoscope apparatuses, illumination light is sequentially output through the narrow-band-pass filters to obtain three signals. The three signals obtained by using the illumination light that has passed through the narrow-band-pass filters are processed in a manner similar to the processing on R, G and B signals (RGB signals), while weighting on each of the three signals is changed. Accordingly, spectral images are generated. When such spectral images are used, very fine structures in gasters (stomachs), large vowels (large intestines), or the like, which could not be observed (extracted) in conventional methods, are extracted.
Meanwhile, instead of the plane-sequential method using the narrow-band-pass filters, as described above, a method of forming spectral images by performing operation processing has been proposed (for example, please refer to Japanese Unexamined Patent Publication No. 2003-093336). The operation processing is performed based on image signals obtained by white light. Specifically, a relation between numerical value data representing the color sensitivity characteristic of each of R, G and B and numerical value data representing the spectral characteristic of specific narrow-band-pass filtered light is obtained as matrix data (coefficient sets). Further, spectral image signals that estimate spectral images obtained by passing light through the narrow-band-pass filter are estimated by performing operation on the matrix data and the RGB signals. When the spectral images are generated by performing such operations, it is not necessary to prepare a plurality of filters corresponding to wavelength bands that users need. Further, since it is not necessary to switchably arrange the filters, it is possible to prevent the size of the apparatuses (endoscope apparatuses or systems) from becoming large, and to reduce the cost of the apparatuses.
The characteristic of the narrow-band observation images obtained by illuminating subjects with narrow-band light and that of the spectral estimation images obtained by matrix operations, as described above, are not exactly the same. Therefore, the narrow-band observation images are suitable to observe some kinds of subjects, but the spectral estimation images are more suitable to observe some other kinds of subjects. Hence, it is desirable that the narrow-band observation images and the spectral estimation images are automatically switched, based on the subject, so that optimum images are displayed to observe the subjects.